The present disclosure relates to industrial equipment having different units selectively attachable to each other to jointly perform a desired activity that requires power. More specifically, the present disclosure relates to industrial equipment where a host unit controls the operation of an attachment that requires electrical power to operate.
One example of such equipment is a lift truck carriage that is selectively attachable to an attachment to lift and move cargo, such as crates, paper rolls, etc. from one place to another. Typically, the attachment will include load-engaging members such as forks that raise pallets, clamps that grasp paper rolls, etc. where positioning of the load-engaging members as well as movement of the load is accomplished hydraulically using fluid supplied from a reservoir on the lift truck. Movement of pressurized fluid between the lift truck and the attachment typically occurs in hydraulic lines that extend over a mast of the lift truck to the attachment.
FIGS. 1 and 2, for example, show a lift truck 10 attached to a roll clamp 12 used to clamp and unclamp cylindrical objects such as large paper rolls, using rotatable pivoted arm clamps 14 actuated by hydraulic cylinders 16 and 17. Though FIG. 1 shows only one cylinder 16 and one cylinder 17, the roll clamp 12 may include two cylinders 16 and two cylinders 17, where the cylinders not shown are located behind the cylinders 16 and 17 that are shown. Rotation of the clamps 14 is achieved by a rotator 18, which rotates the clamp bi-directionally about a longitudinal axis in response to a bidirectional hydraulic motor 20. While the roll clamp 12 includes separate cylinders 16 and 17 by which the clamp arms 14 may be independently actuated, some roll clamps have only a single pair of cylinders 16 to actuate one of the clamp arms 14, while the clamp arm 14 not actuated by the cylinders 16 is fixed.
As seen in FIG. 2, hydraulic fluid from a reservoir 24 is exchanged between the lift truck 10 and the roll clamp 12 via two hydraulic lines 26 and 27 that extend over the mast 22 of the lift truck 10. A handle 28 on the lift truck 10 permits an operator to alternately open or close the clamp arms 14 via actuation of the cylinders 16 and 17, and also permits an operator to rotate the clamps 14 in either selected one of a clockwise or counter clockwise direction via a rotator motor 30. A switch 32 located on the handle 28 is used to determine which function (rotation or clamping) is controlled by the handle 28. The switch 32 is integrated into a wireless transmitter 34 that is in communication with a wireless receiver 36 having a corresponding switch 38 in the roll clamp 12. Thus, for example, an operator can wirelessly cause the switch 38 to operate a spring-biased solenoid valve 40 between an open position and a closed position. It should be understood by those of skill in the art that many other operations may be hydraulically enabled, besides opening and closing a clamp, such as raising or lowering a carriage, side-shifting or rolling a carriage, among many other functions common to lift trucks.
In the open position (as depicted in FIG. 2), pressurized fluid is directed from the reservoir 24 in the lift truck 10, through lines 26, 27 and over the mast 22 to operate the rotator motor 30 in either of two rotational directions depending on the position of the handle 28, i.e. by determining the direction of the flow through the lines 26, 27. Conversely, when the operator uses the switch 32 to wirelessly activate the solenoid valve 40, fluid from the reservoir 24 flows through a pilot line 42 to cause selector control valve 44 to redirect fluid from the rotator motor 20 to the clamp cylinders 16 and 17, as shown in FIG. 2. In this configuration, operation of the handle 28 will alternatively extend or retract the cylinders 16 depending on the position of the handle 28, i.e. by determining the direction of the flow through the lines 26, 27. If a third hydraulic function, such as laterally extending the roll clamp frame were also included, a second pilot-operated valve assembly similar to the combination of valves 40 and 44 would be provided for lateral control using an assembly similar to piston and cylinder assemblies 17, together with a second transmitter/receiver set such as 34 and 36, and a second operator-controlled electrical switch 32.
Hydraulically actuated solenoid switches located on remote attachments, such as the valves 40 and 44 shown in FIG. 2, require a non-trivial amount of power to operate—typically more power than can feasibly be transferred over a wireless radio signal. In such cases, one or more solenoid valves are connected to the attachment and have historically been controlled by electrical wires routed between the lift truck and the attachment, over the mast of the lift truck, so that the operator can electrically select which attachment function will be actuated by the single pair of hydraulic lines. The masts, however, often include rigid metal frames that are slidably engaged with each other to provide a telescoping extension for the mast. Designing a mast having these electrical wires is a complicated task, as there may be bearings between the moving frames and the wires, and the wires must be placed proximate the sliding metal frames without interfering with movement of the mast. Even with the most careful design, routing the electrical wires over the lift truck mast to a movable attachment requires exposure of the wires and their connectors to significant hazards, wear, and deterioration, which results in breakage, short-circuiting, corrosion and other problems that require relatively frequent replacement and downtime. Moreover, lift truck electrical systems range from twelve to ninety volts, requiring a variety of special coils for the solenoid valves.
To eliminate the need for electrical wires that extend over the mast of a lift truck, some attachments have been equipped with a power supply such as a battery to operate the solenoid valves, or other devices that require power, on the attachment. Batteries on attachments, though, deplete rather quickly necessitating replacement and/or frequent charging. This can become quite burdensome and/or inefficient, particularly in energy intensive applications that include multiple batteries on each attachment, where each battery requires weekly replacement or downtime for recharging.
One technique used to minimize down time for recharging a battery has been to use inductive coils to transfer power an attachment so as to recharge the battery. One such system is disclosed in Japanese Patent Application 2001-245518 to Tanaka, in which an inductive power transmitter is mounted rigidly to a host vehicle and an inductive power receiver is mounted to the attachment so as to allow power to be conveyed from a power supply on the host vehicle to recharge a battery on the attachment. The battery in turn supplies power to an electronic code reader on the attachment. However, because the attachment and hence the inductive power receiver moves along the mast of the host vehicle, inductive power may be used to recharge the battery only when the inductive power transmitter and inductive power receiver are aligned with each other. While this arrangement allows the battery to recharge somewhat during operation of the attachment, without necessitating wires over the mast of the host vehicle, the ability to recharge the battery is limited. Thus, while Tanaka's inductive recharging system may be used effectively to recharge a battery that powers small loads, such as the electronic code reader disclosed by Tanaka, it would not eliminate the need for replacement of the battery (or extensive downtime for recharging) when the attachment draws power from a battery to operate more energy intensive loads such as the solenoid switches in the attachment shown in FIGS. 1 and 2, for example.
What is desired, therefore, is improved systems and methods for delivering electrical power so as to operate electromechanical equipment on remote attachments, such as lift truck load handlers, without requiring wires or harnesses over a mast.